JavaScript type simple Description _ Basics

The original type is stored directly on the stack (stack), and the reference type is stored on the heap (heap).

The original type is divided into the following 5 kinds: Undefined, Null, Boolean, number, String

Undefined type:

The undefined type has only one value: undefined. When declaring a variable uninitialized, its default value is: undefined.

When a function does not explicitly return a value, the value returned is also: undefined

Null type:

Null type has only one value: null. The value undefined is actually derived from the value null, so the ECMAScript definition is equal:

alert (null==undefined);//outputs: "True"

Null and undefined values are equal, the meaning of the expression is different: undefined is declared when the variable is not initialized, the assigned value; Null represents an object that does not exist, such as a function returns an object, the object is not found, the return is null.

Boolean type:

Boolean type has 2 values: True and False

Number type:

The number type can represent a 32-bit integer or a 64-bit floating-point number.

Integers by default are 10, or 8 (the first number is 0, such as 070, 10 into 56), 16 (the first 2 is 0x, such as 0xAB, corresponding to 10 into 171).

Regardless of how the number is represented, the result of the operation is the 10 binary result.

To define a floating-point number, you must have a decimal point and a 1-digit decimal place after the dot, such as Var f=2.0. The storage of floating-point numbers is stored as strings.

String type:

Strings are declared with double quotes (") or single quotes (').